Traces of radioactive iodine have been found in milk from San Luis Obispo, but officials say the amounts are so small that they pose no risk.
"People need to realize that really trace amounts do not pose a threat to public health," said Mike Sicilia, a spokesman for the California Department of Public Health. "The levels we detected are nearly 5,000 times less than FDA standards."
The radioactive material is iodine-131, which is produced by nuclear fission. It hadn't been found in California milk samples before fallout from Japan's ravaged Fukushima Daiichi nuclear power plant drifted across the Pacific.
Scientists this week detected a similar amount in milk from the Spokane, Wash. area.
Michael Payne, a veterinarian who heads the Western Institute for Food Safety and Security at UC Davis, called the iodine traces inconsequential.
"I would drink those milk samples without a second thought," he said.
The state tests milk for radioactivity in San Luis Obispo, where cows graze not far from the Diablo Canyon nuclear power plant, and in Humboldt County, where a nuclear plant was shuttered in 1976. There are no major dairies near the San Onofre nuclear plant in northern San Diego County, officials said.
The San Luis Obispo County cows are part of a dairy herd owned by Cal Poly San Luis Obispo. Their milk, which is used commercially, continues to be safe, said Dr. Penny Borenstein, the county's health officer.
"There has been no recall, nor should there be," she said.